Hydrodynamic retarder for vehicles

ABSTRACT

A hydrodynamic retarder for vehicles, especially motor vehicles which includes an internal working circulation between a rotating and a stationary bladed wheel within a working space and an external cooling circulation with a by-pass valve; the filling of the working circulation takes place from a filling cylinder actuated by pressure medium and controlled by a control valve, for example by the brake pedal; the sealed space located directly in front of the shaft seal within the retarder housing is relieved toward a place of the working circulation that is pressureless during operation while a supply tank for working liquid is provided which is connected with the cooling circulation by way of a first check valve that opens in the direction toward the cooling circulation and with the relief line, connecting the space in front of the shaft seal with the working space, by way of a second check valve which closes in the direction toward the relief line.

United States Patent 1 Hanke et al.

[ HYDRODYNAMIC RETARDER FOR VEHICLES Inventors: Hans Hanke; WolfgangPeter, both of Stuttgart, Germany 17, 11 9fi Haida-Egg Ak sege ollsslzeft [22] Filed: Jan. 17, 1972 21 Appl. No.: 218,222

[58] Field of Search 188/290, 296; 277/59; 415/112; 60/337, 339, 347

[56] References Cited UNITED STATES PATENTS 3,146,863 9/1964 Herbenar etal 188/290 X 1,737,870 12/1929 Telfer 415/112 X 3,330,386 7/1967 Bertramet a1... 188/296 3,373,847 3/1968 Rohacs 188/290 X PrimaryExaminer-George E. A. Halvosa AttorneyPaul M. Craig, Jr. et al.

[57] ABSTRACT A hydrodynamic retarder for vehicles, especially motorvehicles which includes an internal working circulation between arotating and a stationary bladed wheel within a working space and anexternal cooling circulation with a by-pass valve; the filling of theworking circulation takes place from a filling cylinder actuated bypressure medium and controlled by a control valve, for example by thebrake pedal; the sealed space located directly in front of the shaftseal within the retarder housing is relieved toward a place of theworking circulation that is pressureless during operation while a supplytank for working liquid is provided which is connected with the coolingcirculation by way of a first check valve that opens in the directiontoward the cooling circulation and with the relief line, connecting thespace in front of the shaft seal with the working space, by way of asecond check valve which closes in the direction toward the relief line.

31 Claims, 1 Drawing Figure 1 HYDRODYNAMIC RETARDER FOR VEHICLES Thepresent invention relates to a hydrodynamic retarder for vehicles,especially motor vehicles, including an internal working circulatorysystem between at least one rotating blade wheel and at least onestationary blade wheel within a working space and an external coolingcirculatory system with a by-pass valve and possibly a cooler wherebythe filling of the working circulatory system takes place from a fillingmedium cylinder actuated by a pressure medium and controlled by acontrol valve, for example, the brake pedal, and whereby the sealedspace directly in front of the shaft seal within the retarder housing isrelieved toward a place in the working circulatory system which ispressureless during operation.

It has already been proposed to construct a hydrodynamic retarder in theaforementioned manner. In contradistinction to retarders with a fillingpump, very short filling periods and a very accurate metering of thebrake moment to be obtained can be achieved thereby. Additionally it isavoided by the construction according to this prior proposal that thesael is overloaded and possibly can even be pushed out.

The present invention is concerned with a further development of thisarrangement, advantageous as such. In particular, it is to be achievedby the present invention that in case of leakage losses in the system,no reduction of the filling quantity and as a result thereof noreduction of the brake moment occurs during a repeating of the brakingoperation. Additionally, it is to be achieved in a simple manner thatalso during standstill the seal cannot be pushed out upon actuation ofthe control valve. The last-mentioned problem has already been solvedalso in the prior proposal, however, the solution of this prior proposalrequires a connection back with the actuating pedal which purely from astructural point of view leads to considerable changes and to a furtherspace requirement.

The underlying problems are solved according to the present inventionwith retarders of the aforementioned type in that a supply tank ofreservoir for working fluid is provided which is connected with thecooling circulatory system by way of a first check valve opening in caseof flow in the direction toward the cooling circulatory system and withthe relief line by a second check valve closing in case of flow in thedirection toward the relief line. it is thereby particularly appropriateif according to a further development of the inventive concept thesupply tank is so arranged that its level is located above the retarderand filling cylinder.

With the retarder proposed in accordance with the present invention anadequate braking effect can also be still realized when a slight leakageloss occurs in the system, or if air should have penetrated into thesystem as a result of a vacuum. Furthermore, a pushing-out" of the sealin standstill is impossible in the arrangement according to the presentinvention whereby the operating realiability and safety is increased.

A further proposal of the present invention is to the effect that atwo-way valve be arranged in parallel with the first check valve,constructed as relief valve, between the supply tank and the coolingcirculatory system, which two-way valve in the idling position of theretarder is open and is adapted to be closed in dependence on thebraking operation shortly before or at the latest when the fillingcylinder responds. It is achieved thereby that the possibly excessivefluid quantity can flow off without resistance into the supply tank.

The control of this two-way valve can take place by conventional meansin a pneumatic, mechanical or similar manner. However, the presentinvention thereby prefers a solution according to which a solenoid valveis provided as two-way valve, closing when energized by a current flow,in the energizing circuit of which is connected a switch closing uponactuation of the control valve for the filling cylinder. This switch ispreferably located therefore at the brake pedal and responds earlierthan the reducing valve to be actuated by the brake pedal for theactuation of the filling cylinder. In another embodiment of the presentinvention the side of the filling cylinder actuated by the pressuremedium is connected with the control member of the two-way valve. Thiscontrol member may be constructed, for example, as diaphragm and may acton the two-way valve either directly or indirectly, for example, againby way of an electric switch.

A further feature of the present'invention resides in that the spring ofthe first check valve, i.e., preferably of the relief valve is soselected and adjusted that also with a closed two-way valve a flow ofworking fluid from the supply tank into the filling cylinder ispossible. Furthermore, it is additionally proposed that the spring ofthe second check valve is adjusted to the maximum permissive pressurefor the seal or to a value slightly below the same.

According to a further development of the inventive concept the springside of the by-pass valve arranged in the cooling circulatory system isconnected with the line between the second check valve and the supplytank. An eventual pressure build-up at the by-pass valve is avoided withcertainty in this manner and above all the leakage fluid is fed back tothe supply tank and is made re-usable in this manner.

Furthermore, provision is additionally made in accordance with thepresent invention that the filling cylinder is constructed as piston ordiaphragm accumulator actuated by pressurized air and is combined into astructural unit together with the supply tank as well as with the twocheck valves and the two-way valve. The operating safety and reliabilityof the installation can be still further increased if according to thepresent invention a conventional float is arranged in the supply tankand is connected with a switching device in such a manner then that awarning signal disposed within the field of view of the driver islighted up when the liquid level drops below a minimum value. Of course,in lieu of or in addition to this optical warning installation also anacoustic warning installation may be provided with approximately thesame means.

Accordingly, it is an'object of the present invention to provide ahydrodynamic retarder for vehicles, especially for motor vehicles whichavoids by simple means the aforementioned shortcomings and drawbacksencountered in the prior art.

Another object of the present invention resides in a hydrodynamicretarder in which no reduction of the filling quantity and consequentlyno reduction of the braking moment occurs when the braking operation isrepeated, notwithstanding leakage losses in the system.

A further object of the present invention resides in a hydrodynamicretarder for vehicles, especially motor vehicles, in which a pushing-outof the seal during standstill upon actuation of the control valve iseffectively precluded.

A still further object of the present invention resides in ahydrodynamic retarder system for vehicles which is simple from astructural point of view and minimizes the space requirements.

Another object of the present invention resides in a hydrodynamicretarder for vehicles, especially motor vehicles which excels byexceptionally high operating safety.

These and further objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in connection with the accompanying drawing which shows, forpurposes of illustration only, one embodiment in accordance with thepresent invention, and wherein:

The single FIGURE is a schematic view, partially in cross section, of ahydrodynamic retarder for vehicles in accordance with the presentinvention.

Referring now to the single figure of the drawing, the retardergenerally designated by reference numeral includes as stator astationary. blading l1 and as rotor a rotating blading 12 'which isdriven from the drive shaft 13. The working space 14 of the retarder 10is provided at the outer circumference with a scroll case 15, to whichis connected the external circulation 16 that again terminates at theinner circumference in the working space 14 and into which are connectedthe cooler 17 of conventional construction and the by-passvalve'generally designated by reference numeral 18. The by-pass valve 18interrupts the external cooling circulatory system 16 when the latter ispressureless so that the external cooling circulation cannot emptyitself.

The shaft 13 is sealed with respect to the retarder housing by a seal 19of conventional construction. A space 20 is disposed directly in frontof the seal 19, which is sealed with respect to the working space 14 bya further contact-free seal 21 of conventional type. This space 20 isrelieved by way of the bores 22 and 23 toward a place of the workingspace 14, where no pressure prevails also during operation. For thatpurpose the relief bore 23 must terminate above the center point of thevertical center section of the working space 14 in such a manner thatthis vertical center section is subdivided in the radial directionapproximately at the ratio of 8:5.

The external circulatory system 16 is connected by way of a line 24 withthe filling cylinder generally designated by reference numeral 25 whichis supplied with compressed air from a reducing valve 27 by way of theline 26; the reducing valve 27, in turn, is actuated by the brake pedal28. The line 24 serves both for the purpose of filling as also for thepurpose of emptying or discharging the cooling circulation 16 as well asof the working space 14. The filling cylinder 25 is constructed asspring-loaded piston accumulator.

The arrangement described so far is either known as such in its detailsor has already been proposed before and therefore does not form any partof the present invention.

In addition to the filling cylinder 25 a supply tank or reservoir 29 isprovided in the installation according to the present invention which isappropriately so arranged that its liquid level lies above the retarderl0 and the filling cylinder 25. This supply reservoir 29 is connected bymeans of the line 30 and by way of the relief valve generally designatedby reference numeral 31 with the filling and discharge line 24. Asolenoid valve generally designated by reference numeral 33 which closeswhen energized by current, is connected in parallel to the check valve31 within a line 32. The relief valve 31, as to the rest, is soconstructed that it permits a flow from the supply tank 29 into the line24 whereas it essentially blocks the retum-flow.

A switch 35 coordinated to the brake pedal 28 is arranged in theenergizing circuit 34 of the solenoid valve 33. The energizing winding(not shown) of the solenoid valve 33 therefore receives current duringthe actuation of the brake pedal 28, and the valve 33 closes. Thisclosing takes place shortly before or at the latest during the pressurebuild-up at the filling cylinder 25 so that in practice the line 32 isalready closed when the filling cylinder 25 feeds by way of the line 24into the cooling circulation 16 and the working space 14.

A further branch line 36 branches off from the line 30 between thesupply reservoir 29 and the relief valve 31. This further line 36 leadsto the relief bore 23 by way of a second check valve generallydesignated by reference numeral 37. This check valve 37 permits a flowfrom the relief bore 23 in the direction toward the supply tank 29whereas it blocks a flowin the opposite direction. The spring-loadedside of the by-pass valve 18 is connected by way of the line 38 with theline 36 between the check valve 37 and the supply reservoir 29.

It should be mentioned that the spring force at the relief valve 31 isso adjusted that also with a closed solenoid valve 33 the fillingcylinder 25 is able to fill itself by suction effect from the supplytank 29 by way of the lines 30 and 24. This means this spring isrelatively weak. in contradistinction thereto, at the check valve 37 thespring is so adjusted that it lies below the maximum pressure of theseal 19 or at most attains the same. i

During standstill of the vehicle the working space 14 is empty orpressureless. The by-pass valve 18 is thereby in the illustrated closingposition. The filling cylinder 25 is filled with working liquid. lf nowthe brake pedal 28 is actuated inadvertently or, for example, forpurposes of testing, then at first the solenoid valve 33 is closed andimmediately' thereafter the working space 14 is placed under pressure inthe usual manner from the filling cylinder 25 byway of the line 24. Thispressure can'be relieved from the space 20 arranged in front of the seal19 by way of the relief bores 22 and 23 as well as the check valve 37and the line 36 in the direction toward the supply tank 29 so that theseal 19 under no circumstances is damaged or pushed out.

A closing of the line 32, as to the rest, can also be achieved if inlieu of the solenoid valve 33 and in lieu of the energizing circuit 34appertaining thereto, a valve actuated by pressure medium is providedwhose control member, for example, a diaphragm is connected by way ofthe line 39 indicated in dash and dot lines with the line 26 between thefilling cylinder 25 and the reduction valve 27.

During operation of the vehicle the starting condition is again the sameas described above, i.e., the working space 14 is empty andpressureless. lf now the brake pedal 28 is again actuated, then thesolenoid valve 33 is closed in the manner already described and apredetermined pressure build-up corresponding to the position of thebrake pedal 28 is achieved from the filling cylinder 25 in the workingspace 14. As a result thereof a predetermined filling and consequentlyalso a predetermined brake moment is adjusted. The working fluid therebycirculates constantly in the external circulatory system 16 because as aresult of the pressure within the same the by-pass valve 18 is now open.If in this condition the pressure from the filling cylinder is takenaway, i.e., if the actuation of the brake pedal 28 stops, then theretarder will be emptied by way of the line 24 as a result ofcentrifuging action and the filling cylinder 25 again is filled.

It may now happen that leakage losses occur at the retarder 10 or in thecooling circulation 16. In this case, the constant filling quantity ofthe filling cylinder 25 would then no longer suffice to completely fillthe retarder l0 and the cooling circulation 16 so that only a smallerbrake moment could be still absorbed. In case of further leakage lossesthis condition would continuously deteriorate. However, this isprevented in the system of the present invention in that during eachemptying of the working circulation l4 and of the cooling circulation 16the filling cylinder 25 fills itself again completely out of the supplytank 29 by suction action by way of the relief valve 311 and the lines30 and 24. Consequently, the completely filled filling cylinder 25 isagain available during the next braking operation. The check valve 31and the solenoid valve 33 assure that during the braking the filling ofthe filling cylinder 25 is, in fact, supplied to the working space 14and to the cooling circulation 16 and is not received, for example, inthe supply tank 29.

The supply tank 29 may also be provided with a conventional floatgenerally designated by reference numeral 40 for indicating when theliquid level thereof drops below a predetermined level. The float 40includes a float member 41- pivotally mounted at 42 and a contact 43adapted to make a ground connection with ground terminal 44 when theminimum liquid level is reached. A warning device, such as a lamp 47 oracoustic device is connected in a circuit 45 including the switchcontact 43 and a voltage supply source 46 connected with one terminal toground so that when the switch contact 43 establishes a groundconnection with terminal 44, the lamp 47 starts to light up.

While we have shown and described only one embodiment in accordance withthe present invention, it is understood that the same is not limitedthereto but is susceptible of numerous changes and modifications asknown to those skilled in the art and we therefore do not wish to belimited to the details shown and described herein but intend to coverall such changes and modifications as are encompassed by the scope ofthe appended claims.

What we claim is:

1. A hydrodynamic retarder installation comprising:

a brake housing;

at least one fixed blade wheel and one rotatable blade wheel arranged inspaced facing relationship to one another in said housing;

a working fluid circulatory system for supplying working fluid to aworking chamber formed between said fixed and rotatable blade wheels toeffect braking of a shaft connected to said rotatable blade wheel;

brake actuating means for controlling said supply of working fluid tosaid working chamber;

a shaft seal interposed between said housing and said shaft to limitescape of working fluid from said housing along said shaft;

first conduit means for directly communicating the core of said workingchamber with a seal space between said housing and said shaft which issealed off by the shaft seal such that the low pressure experienced atsaid core during supply of working fluid with a rapidly rotating shaftrelieves said shaft seal;

supply tank means containing a supply of working fluid;

second conduit means for communicating said supply tank means with saidworking fluid circulatory system by way of a first check valve meanswhich permits flow through said second conduit means from said supplytank means to said working fluid circulatory system and which preventsflow through said second conduit means from said working fluidcirculatory system to said supply tank means, whereby working fluid canbe supplied to said working fluid circulatory system by way of saidfirst check valve means without backflow from said working fluidcirculatory system to said supply tank means through said second conduitmeans;

and third conduit means for communicating said supply tank means withsaid first conduit means by way of a second check valve means whichprevents flow throughsaid third conduit means from said supply tankmeans in a direction toward said core and seal space and which permitsflow through said third conduit means from said core and seal space tosaid supply tank means, whereby an excessive pressure build-up in saidseal space is automatically limited by said second check valve meanspermitting fluid flow from said seal space to said supply tank means.

2. A retarder installation according to claim 1, further comprising anexternal cooling circulatory means having a cooler and a by-pass valvemeans, said cooling circulatory means being connected to said workingfluid circulatory system for cooling the working fluid.

3. A retarder installation according to claim 1, characterized in thatthe second check valve means includes a spring which is adjusted atmost'to the maximum permissive pressure of the seal means.

4. A retarder installation according to claim 1, characterized in that afloat means is arranged in the supply tank means which is so connectedwith a switch means that a warning signal appears in the field of visionof the driver when the liquid level in the supply tank means drops belowa predetermined minimum level.

5. A retarder installation according to claim 6, further comprising anexternal cooling circulatory means having a cooler and a by-pass valvemeans, said cooling circulatory means being connected to said workingfluid circulatory system for cooling the working fluid.

6. A retarder installation according to claim 1, wherein the brakeactuating means includes a filling cylinder means actuable in responseto a pressure medium and control valve means for controlling thepressure medium for actuating said filling cylinder means.

7. A retarder installation according to claim 6, wherein the supply tankmeans is positioned with the level of working fluid therein normallyabove both the working chamber and the filling cylinder means.

8. A retarder installation according to claim 7, characterized in that atwo-way valve means is arranged be tween the supply tank means and thecooling circulatory means in parallel to the first check valve means,said two-way valve means being open in the idling nonbraking position ofthe retarder installation and being operable to be closed as a functionof the braking operation at the latest upon response of the fillingcylinder means.

9. A retarder installation according to claim 8, characterized in thatthe two-way valve means is closed in dependence of the braking operationshortly before the response of the filling cylinder means.

10. A retarder installation according to claim 8, characterized in thatthe first check valve means is constructed as relief valve.

1 1. A retarder installation according to claim 8, characterized in thata solenoid valve is provided as the twoway valve means which closes uponenergization thereof and which includes an energizing circuit providedwith a switch closing upon actuation of the control valve means for thefilling cylinder means.

12. A retarder installation according to claim 8, characterized in thatthe two-way valve means includes a control member andin that a side ofthe filling cylinder means actuated by the pressure medium is connectedwith the control member of the two-way valve means.

13. A retarder installation according to claim 8, characterized in thatthe first check valve means includes a spring which is so adjusted thata flow and refilling of working liquid from the supply tank means intothe filling cylinder means is posible also with a closed two-way valvemeans.

14. A retarder installation according to claim 13, characterized in thatthe second check valve means includes a spring which is adjusted at mostto the maximum permissive pressure of the shaft seal.

15. A retarder installation according to claim 14, characterized in thatthe spring of the second check valve means is adjusted slightly belowthe maximum permissive pressure of the shaft seal.

16. A retarder installation according to claim 14, characterized in thatthe spring side of the by-pass valve means is connected with a linebetween the second check valve means and the supply tank means.

17. A retarder installation according to claim 14, characterized in thata spring side of the by-pass valve means is connected with a linebetween the second check valve means and the supply tank means.

18. A retarder installation according to claim 17, characterized in thatthe supply tank means as well as the two check valve means and thetwo-way valve means are combined into a structural unit.

19. A retarder installation according to claim 18, characterized in thatthe filling cylinder means is constructed as a piston accumulatoractuated by compressed air.

20. A retarder installation according to claim 18, characterized in thatthe filling cylinder means is constructed as a diaphragm accumulatoractuated by compressed. air.

21. A retarder installation according to claim 18,

characterized in that a float means is arranged in the supply tank meanswhich is so connected with a switch means that a warning signal appearsin the field of vision of the driver when the liquid level in the supplytank means drops below a predetermined minimum level.

22. A retarder installation according to claim 21, characterized in thata solenoid valve is provided as the two-way valve means which closesupon energization thereof and which includes an energizing circuitprovided with a switch closing upon actuation of the control valve meansfor the filling cylinder means.

23. A retarder installation according to claim 21, characterized in thatthe two way-valve means includes a control member and in that a side ofthe filling cylinder means actuated by the pressure medium is connectedwith the control member of the two-way valve means.

24. A retarder installation according to claim 6, wherein said controlvalve means is controlled by brake pedal means.

25. A retarder installation according to claim 24, further comprising anexternal cooling circulatory means having a cooler and a by-pass valvemeans, said cooling circulatory means being connected to said workingfluid circulatory system for cooling the working fluid.

26. A retarder installation according to claim 25, characterized in thata two-way valve means is arranged between the supply tank means and thecooling circulatory means in parallel to the first check valve means,said two-way valve means being open in the idling non-braking positionof the retarder installation and being operable to be closed as afunction of the braking operation at the latest upon response of thefilling cylinder means.

27. A retarder installation according to claim 26, characterized in thatthe two-way valve means is closed in dependence of the braking operationshortly before the response of the filling cylinder means.

28. A retarder installation according to claim 26, characterized in thata solenoid valve is provided as the two-way valve means which closesupon energization thereof and which includes an energizing circuitprovided with a switch closing upon actuation of the control valve meansfor the filling cylinder means.

29. A retarder installation according to claim 26, characterized in thatthe two-way valve means includes a control member and in that the sideof the filling cylinder means actuated by the pressure medium isconnected with the control member of the two-way valve means.

30. A retarder installation according to claim 26, characerized in thatthe first check valve means includes a spring which is so adjusted thata flow and refilling of working liquid from the supply tank means intothe filling cylinder means is possible also with a closed two-way valvemeans.

31. A retarder installation according to claim 26, characterized in thatthe supply tank means as well as the two check valve means and thetwo-way valve means are combined into a structural unit.

1. A hydrodynamic retarder installation comprising: a brake housing; atleast one fixed blade wheel and one rotatable blade wheel arranged inspaced facing relationship to one another in said housing; a workingfluid circulatory system for supplying working fluid to a workingchamber formed between said fixed and rotatable blade wheels to effectbraking of a shaft connected to said rotatable blade wheel; brakeactuating means for controlling said supply of working fluid to saidworking chamber; a shaft seal interposed between said housing and saidshaft to limit escape of working fluid from said housing along saidshaft; first conduit means for directly communicating the core of saidworking chamber with a seal space between said housing and said shaftwhich is sealed off by the shaft seal such that the low pressureexperienced at said core during supply of working fluid with a rapidlyrotating shaft relieves said shaft seal; supply tank means containing asupply of working fluid; second conduit means for communicating saidsupply tank means with said working fluid circulatory system by way of afirst check valve means which permits flow through said second conduitmeans from said supply tank means to said working fluid circulatorysystem and which prevents flow through said second conduit means fromsaid working fluid circulatory system to said supply tank means, wherebyworking fluid can be supplied to said working fluid circulatory systemby way of said first check valve means without backflow from saidworking fluid circulatory system to said supply tank means through saidsecond conduit means; and third conduit means for communicating saidsupply tank means with said first conduit meAns by way of a second checkvalve means which prevents flow through said third conduit means fromsaid supply tank means in a direction toward said core and seal spaceand which permits flow through said third conduit means from said coreand seal space to said supply tank means, whereby an excessive pressurebuild-up in said seal space is automatically limited by said secondcheck valve means permitting fluid flow from said seal space to saidsupply tank means.
 2. A retarder installation according to claim 1,further comprising an external cooling circulatory means having a coolerand a by-pass valve means, said cooling circulatory means beingconnected to said working fluid circulatory system for cooling theworking fluid.
 3. A retarder installation according to claim 1,characterized in that the second check valve means includes a springwhich is adjusted at most to the maximum permissive pressure of the sealmeans.
 4. A retarder installation according to claim 1, characterized inthat a float means is arranged in the supply tank means which is soconnected with a switch means that a warning signal appears in the fieldof vision of the driver when the liquid level in the supply tank meansdrops below a predetermined minimum level.
 5. A retarder installationaccording to claim 6, further comprising an external cooling circulatorymeans having a cooler and a by-pass valve means, said coolingcirculatory means being connected to said working fluid circulatorysystem for cooling the working fluid.
 6. A retarder installationaccording to claim 1, wherein the brake actuating means includes afilling cylinder means actuable in response to a pressure medium andcontrol valve means for controlling the pressure medium for actuatingsaid filling cylinder means.
 7. A retarder installation according toclaim 6, wherein the supply tank means is positioned with the level ofworking fluid therein normally above both the working chamber and thefilling cylinder means.
 8. A retarder installation according to claim 7,characterized in that a two-way valve means is arranged between thesupply tank means and the cooling circulatory means in parallel to thefirst check valve means, said two-way valve means being open in theidling non-braking position of the retarder installation and beingoperable to be closed as a function of the braking operation at thelatest upon response of the filling cylinder means.
 9. A retarderinstallation according to claim 8, characterized in that the two-wayvalve means is closed in dependence of the braking operation shortlybefore the response of the filling cylinder means.
 10. A retarderinstallation according to claim 8, characterized in that the first checkvalve means is constructed as relief valve.
 11. A retarder installationaccording to claim 8, characterized in that a solenoid valve is providedas the two-way valve means which closes upon energization thereof andwhich includes an energizing circuit provided with a switch closing uponactuation of the control valve means for the filling cylinder means. 12.A retarder installation according to claim 8, characterized in that thetwo-way valve means includes a control member and in that a side of thefilling cylinder means actuated by the pressure medium is connected withthe control member of the two-way valve means.
 13. A retarderinstallation according to claim 8, characterized in that the first checkvalve means includes a spring which is so adjusted that a flow andrefilling of working liquid from the supply tank means into the fillingcylinder means is posible also with a closed two-way valve means.
 14. Aretarder installation according to claim 13, characterized in that thesecond check valve means includes a spring which is adjusted at most tothe maximum permissive pressure of the shaft seal.
 15. A retarderinstallation according to claim 14, characterized in that the spring ofthe second check valve means is adjusted slightly below the maximumpermissive pressure of the shaft seal.
 16. A retarder installationaccording to claim 14, characterized in that the spring side of theby-pass valve means is connected with a line between the second checkvalve means and the supply tank means.
 17. A retarder installationaccording to claim 14, characterized in that a spring side of theby-pass valve means is connected with a line between the second checkvalve means and the supply tank means.
 18. A retarder installationaccording to claim 17, characterized in that the supply tank means aswell as the two check valve means and the two-way valve means arecombined into a structural unit.
 19. A retarder installation accordingto claim 18, characterized in that the filling cylinder means isconstructed as a piston accumulator actuated by compressed air.
 20. Aretarder installation according to claim 18, characterized in that thefilling cylinder means is constructed as a diaphragm accumulatoractuated by compressed air.
 21. A retarder installation according toclaim 18, characterized in that a float means is arranged in the supplytank means which is so connected with a switch means that a warningsignal appears in the field of vision of the driver when the liquidlevel in the supply tank means drops below a predetermined minimumlevel.
 22. A retarder installation according to claim 21, characterizedin that a solenoid valve is provided as the two-way valve means whichcloses upon energization thereof and which includes an energizingcircuit provided with a switch closing upon actuation of the controlvalve means for the filling cylinder means.
 23. A retarder installationaccording to claim 21, characterized in that the two way-valve meansincludes a control member and in that a side of the filling cylindermeans actuated by the pressure medium is connected with the controlmember of the two-way valve means.
 24. A retarder installation accordingto claim 6, wherein said control valve means is controlled by brakepedal means.
 25. A retarder installation according to claim 24, furthercomprising an external cooling circulatory means having a cooler and aby-pass valve means, said cooling circulatory means being connected tosaid working fluid circulatory system for cooling the working fluid. 26.A retarder installation according to claim 25, characterized in that atwo-way valve means is arranged between the supply tank means and thecooling circulatory means in parallel to the first check valve means,said two-way valve means being open in the idling non-braking positionof the retarder installation and being operable to be closed as afunction of the braking operation at the latest upon response of thefilling cylinder means.
 27. A retarder installation according to claim26, characterized in that the two-way valve means is closed independence of the braking operation shortly before the response of thefilling cylinder means.
 28. A retarder installation according to claim26, characterized in that a solenoid valve is provided as the two-wayvalve means which closes upon energization thereof and which includes anenergizing circuit provided with a switch closing upon actuation of thecontrol valve means for the filling cylinder means.
 29. A retarderinstallation according to claim 26, characterized in that the two-wayvalve means includes a control member and in that the side of thefilling cylinder means actuated by the pressure medium is connected withthe control member of the two-way valve means.
 30. A retarderinstallation according to claim 26, characerized in that the first checkvalve means includes a spring which is so adjusted that a flow andrefilling of working liquid from the supply tank means into the fillingcylinder means is possible also with a closed two-way valve means.
 31. Aretarder installation according to claim 26, characterized in that thesupply tank means as well as the two check valve means and the two-wayvalve means are combined into a structural unit.